Igniter



IGNITER Filed March 19, 1945 ze/m 7% 5w 0 2 m g/g ey Patented Dec. 27,1949 IGNITER Henry J. De N. McCollum, deceased, late of Chicago, 111.,by Thelma McCollum, executrix, Chicago, 111., assignor to Stewart-WarnerCorporation, Chicago, 111., a corporation of Virginia Application March19, 1945, Serial No. 583,617

3 Claims. 1

The invention relates generally to igniters of the electrical resistancewire type such as are particularly adapted for use as parts of varioustypes of combustion apparatus, for example, oil, gas, and gasolineburning heaters for. use in vehicles as well as in stationaryinstallations.

In burners for-the combustion of gasoline, oil, and gas, it has becomecommon practice to use an igniter of the electrical resistance wiretype, usually in the form of a coil of high resistance wire, located inor adjacent the combustion chamber, and heat it to incandescence bypassing an electrical current therethrough. In burners used in heatinginstallations in which a low volttage current source is available suchas the 6 volt storage battery of an automobile, the igniter wire may beof reasonable gauge (diameter) and length so that the coil into which itis formed may be of dimensions favorable to prompt and effectiveignition of the fuel mixture in the combustion chamber. After combustionhas been established, it is the customary practice to deenergize theigniter, not only to relieve the load on the electrical energy source,but also to reduce the temperature of the igniter and thus extend itsuseful life.

Under such use of an igniter of this type, the surfaces of the igniterwire coil may be at a lower temperature than other parts in or adjacentthe combustion chamber, and if the combustion of fuel is not perfectlycomplete, particles of carbon soot may be deposited upon the wire. Aftersome period of use of the heating apparatus, this deposit of soot uponthe igniter wire coil may become sufficiently thick that the carbonforms a conducting bridge across two or more turns of the coil. Thisreduces the resistance of the bridged turns with the result that thevoltage drop across the remaining turns is increased, and the latterbecome heated to an excessively high temperature. In time, such hightemperatures will cause the igniter coil to burn ou due to oxidation andvaporization of the wire.

This problem of providing an electrical resistance wire igniter whichwill have a long useful life, is accentuated when it is endeavored tomake an igniter of this type which will operate from a higher voltagesource such, for example, as the 24 volt system commonly employed inaircraft. It has been found that the portion of the igniter wire whichis exposed to the flow of the fuel mix-, ture and products of combustionis preferably of certain dimensions. If there is a substantial departurefrom these dimensions, oxidation of the igniter wire coil takes placequite rapidly with a resultant early failure of the igniter. Some of thefactors which have been found appreciably to affect the useful life ofthe igniter relate to the gaug of the wire,'-the diameter of the coil,the

spacing of the turns of the coil, the emissivity of the coil due to thecharacter of its surface finish, the surface finish of the shellsurrounding the coil, the distance of this shell from the coil, as wellas the composition of the alloy of which the resistance wire is made.These factors have been found to be so critical in the design of a lowvoltage (6 volt) igniter that it was deemed advisable, in theconstruction of an igniter for a 24 volt source, to utilize an ignitioncoil of the dimensions found to be practical, and to provide a ballastcoil for obtaining the desired 18 volt potential drop necessary to theapplication of a 6 volt potential to the ignition portion of the coil.However, igniters employing such ballast coil exposed to the flow offuel mixture and products of combustion, rapidly became covered withcarbon, as previously described, with the result that these ignitersfailed after unsatisfactorily short periods of use.

It is thus an object of the invention to provide an improved electricaligniter having a ballast coil to secure the necessary voltage upon theignition coil, in which access of fuel vapor and products of combustionto the wire of th ballast coil is substantially prevented, with theresult that the ballast coil maintains a generally uniform overallresistance throughout the life of the igniter and the igniter coiltherefore has the voltage for which the coil was designed, impressedthereon throughout the life of the igniter.

A further object is to provide an improved igniter structure including ashell, in which is located a ballast coil as well as the igniter coil.

A further object is to provide an improved igniter for operation atrelatively high voltages, which is small and compact.

A further object is to provide an igniter structure employing an ignitercoil and a ballast coil in a unitary structure, in which the heatgenerated in the ballast coil is effectively utilizable for thevaporization of fuel.

A further object is to provide an improved igniter structure which maybe quickly and easily assembled, which will have a long useful life, andwhich may be operated at relatively high impressed voltages.

Other objects will appear from the following description, referencebeing had to the accompanying drawings, in which:

Fig. 1 is a side elevational view of a complete igniter, shown to asomewhat enlarged scale;

Fig. 2 is a central longitudinal sectional view of the igniter, shown toa greatly enlarged scale; and

Fig. 3 is a transverse sectional view thereof, taken on the line 3--3 ofFig. 2.

As best illustrated in Fig. 2, the igniter come prises a shell l0.having an elongated hollow eye 3 lindrical skirt portion l2. The shell Iis provided with a threaded section 14 by which the igniter is securedto the burner, with the skirt portion [2 projecting into the combustionchamher, or a passageway communicating with the combustion chamber. Theshell also has a hexagonal portion l6 for engagement by a wrench, andits head is provided with a noncircular open 1 substantially ing [8 forthe reception of a complementally shaped insulating bushing 22 throughwhich a terminal stud 24 projects. portion 26 which may be square or ofany other suitable noncircular shape, and fits into the similarly shapedopening formed in the bushing 22. The stud 24 has a head 28 which may beformed integrally therewith, the stud preferably being formed by aheading operation. The head 28 and shank 26 have a centrally drilledhole 36 for the reception of the end of a resistance wire 32, which ismounted upon a form 34 having a helical groove upon its external surfacefor the reception of the wire 32. The portion of the wire 32 which iswound upon the form 34 will hereinafter be referred to as the ballastcoil 36.

The wire 32 passes through a radial slot 38 formed in the form 34 andcontinues as a smaller diameter coil 40, hereinafter termed the ignitercoil.

The form 34 is made of a suitable electrical insulating and heatresistant ceramic, such as Isolantite, and has a bore 44 extendingtherethrough, this bore engaging a short projection 46 on the head 28,thus locating its inner end centrally of the shell l0. After the form34, with the wire 32 wound therearound, has thus been inserted in theshell. In, the space surrounding the ballast coil 36 is filled with apowdered Alundum cement 48 (preferably type- RA-305). After the cementhas thus been filled in these spaces, the igniter is tapped so as tocompact the powdered cement, and a loose fitting retaining sleeve 50 isdropped into the end of the shell skirt 12, this sleeve having ashoulder 52 engaging the end of the form 34 so as to locate and hold thelatter in position. After the sleeve 50 is in place, the radiallyextending end portion 56 of the wire 32 is brazed to the end of theskirt portion I2, so as to establish a good electrical contact and limitthe movement of the sleeve i! in the skirt l2. The sleeve 50 has asuitable notch 58 through which the end portion 56 of the wire projects.

A ground wire 62 projects into a suitable drilled hole 64 formed in thehexagonal portion I6 of the shell and is secured therein by a swagingoperation. The stud 24 is insulated from theshell l0, not only by thebushing 22 heretofore described, but also by suitable insulating washers64 and 66. A nut 68 and metal washer 69 are provided for clamping thestud 24 in position. The stud 24 forms the binding post for theattachment of one of the conductors leading to the source of electricalenergy, the other terminal of the source being grounded and thusvconnected to the ground wire 6.2. j

After the igniter has been assembled in the manner described, electricalconnections to a source of electrical energy at a potential of 22 voltsis effected between the wire 62 and the terminal stud 24, and. theigniter thus electrically heated for a period of approximately 45minutes. The resultant heat causes the Alundum cementitious material tocoalesce and form a rigid mass, filling the space between the bore ofthe shell Ill and the. outer suriacerof the ballast coil 36 and Thisstud has a shankits form 34. Thereafter the voltage is increased to 25volts for approximately fifteen minutes, after which the voltage isfurther increased to 25 volts for approximately two minutes. With theparts still hot from these firing operations, the nut 63 is tightened.

The resultant igniter structure is found to be impervious to the fiow ofair through it since the cementitious material forms a seal between theskirt portion l2, the wire 32, and the form 34. Since the portion of thewire 32 forming the ballast coil 36 is thus sealed against the corrosiveinfluences of the products of combustion and the atmosphere, thisballast coil will not deteriorate during long periods of use, and itwill be only the igniter coil 40 which will be subject to oxidation andto a deposit of soot thereon. However, this coil 46 will have a voltageof 6 volts impressed across it when the igniter is connected to a 24volt source and the size of the wire, the spacing and diameter of theturns, is such that such soot deposits do not present a serious problem.

. The inner cylindrical surface of the retaining sleeve 53 is spacedsufficiently from the turns of the igniter coil 46 that the latter isnot locally overheated by heat reflected from the surface of the sleeveto the coil. The igniter coil 46 is of sufiiciently large gauge wire andits turns of sufficiently small diameter that it presents a.non-sagging, rigid element which will retain its form even thoughsubjected to severe shock and vibration when heated to incandescence. Itmay thus be used in aircraft heaters where shock and vibration forcesmay be quite severe.

While a large proportion of the heat generated by the current flowthrough the ballast coil 33 is not permitted to be conducted from thiscoil, due to the heat insulating efiect of the cementitious material 48,s ufiicient heat may be conducted through this material to heat thatportion of the shell l2 which surrounds the ballast coil. Because of thelack of possibility of free radiation of heat from the ballast coil thiscoil may operate at a slightly higher temperature than the igniter coil40, but since the ballast coil is hermetically sealed, its hightemperature does not influence its useful life. The relative resistancesof the ballast coil 36 and the igniter coil 40 are such that whensubjected to a voltage source of 24 volts for a short period of time,the voltage division between the two coils will be such that the voltageacross the igniter coil 40 will be substantially 6 volts.

In using the igniter, the-igniter coil 49, being open to the air, will,upon being supplied with energizing current, evaporate the gasolinebefore a temperature is attained at which carbonization of the gasolinewill take place. Any gasoline which may have penetrated the ceramicmaterial will likewise be vaporized, although at a slower rate. As aresult neither the igniter coil til nor the ballast coil 36 willaccumulate carbon deposits and the useful life of the igniter ismaterially extended.

While a preferred embodiment of the invention has been shown anddescribed, it will be apparent that. numerous variations andmodifications thereof may be .made without departing from the underlyingprinciples of the invention. It is therefore desired, by the followingclaims, to include within the .scope of the invention all suchvariations and modifications by which substantially the results of. theinvention may be obtained through the use of substantially the same orequivalent means.

The invention claimed is:

1. An igniter for the ignition of gaseous and liquid fuels adapted foroperation from the rela tively high potential source of electricalenergy comprising a coil at least half of which constitutes a ballastcoil and the remaining portion of which constitutes an igniter coil, acasing to contain said ballast coil, a refractory ceramic materialmounting the ballast coil within the casing out of contact therewith,said material completely enveloping said ballast coil to exclude saidcoil from atmospheric exposure, the free extremity of said igniter coilbeing connected to said casing, and means for effecting electricalconnection with the free end of said ballast coil and said casing, saidigniter coil being freely suspended and supported by its connections tosaid casing and said ballast coil.

2. An igniter as set forth in claim 1 wherein said casing includes meansfor mounting said igniter within an ignition chamber such that asubstantial portion of said ballast coil lies within said chamber.

3. An igniter for the ignition of gaseous and liquid fuels adapted foroperation from a relatively high potential source of electrical energycomprising a connected ballast coil and an igniter coil, a casing tocontain said coils, a refractory ceramic material filling the portion ofsaid casing containing the ballast coil, said material completelyenveloping said ballast coil to exclude that coil from atmosphericexposure, the free extremity of said igniter coil being connected tosaid casing, and means for effecting electrical connection with the freeend of said ballast coil and said casing, said igniter coil being freelysuspended and supported by the connections to said casing and saidballast coil.

TI-IELMA McCOLLUM, Ezrecutrim of the Last Will and Testament of Henry J.De N. McC'oZZum, Deceased.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 574,536 Hadaway, Jr., Jan. 5,1897 1,590,891 Heaney June 29, 1926 1,655,720 Ziola Jan. 10, 19281,658,990 Keene Feb. 14, 1928 1,826,788 Huber Oct. 13, 1931 1,905,232Kercher et al Apr. 25, 1933 2,126,442 Baud Aug. 9, 1938 2,404,841 Hesset al July 30, 1946

